Many native leggings were made from trade cloth, so the question becomes what trade cloth was traditional in the area and time frame. Where I am from, Osage County Oklahoma, I have seen many leggings made from wool cloth, often dark blue or red, and often decorated (as is typical for Osages) with ribbon work. The ones that I have seen form a perfect rectangle when laid flat and have a seam that runs diagonal in a straight line from ankle to thigh, so there were no curves to get close fitting.
A simple Google image search will show you plenty of variations.
